1. Field of the Invention
The present invention generally relates to an arrangement for treating flora and fauna waste, and more particularly to such an arrangement that treats the garbage by hydrothermal reaction under a subcritical condition.
2. Description of the Related Art
Conventionally, flora and fauna waste such as garbage is collected by vehicles and carried to a particular place so that it is incinerated in a waste disposal facility, buried in the ground or used in reclamation by specialists. In recent years, however, various machines for treating the garbage were developed.
For example, Japanese patent Application, Laid Open publication No. 10-328699 entitled xe2x80x9cSUPERCRITICAL HYDROXYLATION REACTORxe2x80x9dpublished Dec. 15, 1998 discloses an apparatus for oxidizing and dissolving organic waste containing water by supercritical hydroxylation reaction. Specifically, organic sludge is pressurized to more than a supercritical pressure of water (22 Mpa) together with oxygen, and heated to more than a supercritical temperature (374xc2x0 C.). Then, the organic sludge is fed into a reactor for dissolving. At the same time, the oxygen mixed in the organic waste oxidizes the dissolved substances inside the reactor.
However, the above described dissolving and oxidizing method and apparatus requires severe conditions such as supercritical pressure and temperature so that piping and associated parts likely corrode.
Since the dissolving and oxidization take place under the pressure of 22 Mpa or more and the oxidization proceeds simultaneously in the reactor, the temperature rises to about 600xc2x0 C. Thus, the apparatus should be made from a material which is resistive to such high pressure and temperature. In addition, that material must be resistant to the oxidization atmosphere.
Moreover, the organic waste has high viscosity so that it is difficult to continuously pressurize the waste to 22 Mpa or more by a plunger pump or the like.
One of the objects of the present invention is to a waste treating apparatus that can overcome the above described problems. Specifically, the present invention aims to maintain a dissolving capability of a waste treating apparatus while not subjecting the piping to corrosion.
According to one aspect of the present invention, there is provided an apparatus for treating flora and fauna waste, including a preparation unit for mixing the flora and fauna waste with water and chemicals to prepare a starting material (i.e., slurry), a pressuring unit for pressuring the slurry to subcritical pressure of water, a hydrothermal reaction unit for heating the pressurized slurry to cause hydrothermal reaction in a subcritical condition thereby obtaining dissolved waste, and an oxidization unit for oxidizing the dissolved waste after pressure reduction. In the present invention, therefore, the flora and fauna waste undergo the two processes, i.e., the hydrothermal reaction under the subcritical condition, and the oxidation. Thus, the flora and fauna waste can be disposed as sewage. Further, dioxins and other harmful gas are not generated.
The hydrothermal reaction unit may include a hydrothermal reaction tube and a heat medium circuit for heating the hydrothermal reaction tube. The hydrothermal reaction unit may further include a circulation mechanism, which connects an outlet of the hydrothermal reaction tube to an inlet of the reaction tube, for circulating the slurry to the reaction tube. The hydrothermal reaction unit may further include a heat exchanger for heat exchange between the slurry directed to the hydrothermal reaction tube and the dissolved waste directed to the oxidation unit.
The pressurizing unit may include a diaphragm pump for pressurizing the slurry to 6 Mpa or more, which is a subcritical pressure of water.
The oxidation unit may include an oxidation vessel for receiving the dissolved waste from the hydrothermal reaction unit after the dissolved waste is depressurized, and an oxygen supply unit for feeding an oxidizing agent such as air or oxygen to the oxidation vessel such that organic components such as hydrocarbon contained in and associated with the dissolved waste are deconstructed in the oxidation vessel for oxidation.
The oxidation unit may further include a gas-liquid separator located downstream of the oxidation vessel for separating the oxidized waste to a gas component and a liquid component, and a return line for returning the liquid component to the oxidation vessel.